A parosteal lipoma is a benign fatty neoplasm closely related to the periosteum. This report describes a 42-year-old man with parosteal lipoma. He was aware of swelling of his left shoulder since the summer of 2001. In hospitalization, we recognized a tumor with a diameter of about 8cm in his left shoulder which was elastic and soft. We recognized an osseous projection in proximal lesion of his humerus on a simple X-ray image and found fatty lesion surrounding this osseous projection in contact with the humerus in CT and MRI. It was partially enhanced in contrasting MRI. After needle biopsy, we performed tumor excision. A fatty tumor adhered to an osseous projection. In histology, the osseous projection was covered in thick cartilaginous tissue partly like cartilage cap, and osteochondroma was suspected. The differentiation of the merger of a lipoma and osteochondroma, and parosteal lipoma to determine the presence of fibrous tissue is an interesting issue.
